This invention relates generally to condition-responsive controls and, particularly, to a condition-responsive electric switch mechanism having an alarm or an alarm and line switch.
Switches that are responsive to temperature changes, commonly known as thermostats or cold controls, are used in refrigeration appliances, such a refrigerators and freezers, to control the temperatures therein. These thermostats regulate the switching cycle of the refrigeration compressor in response to the temperature of the air contained at some location within the appliance. When the temperature exceeds a certain "turn-on" point, the switch contacts are closed and the compressor is switched on to cool the appliance. When the temperature drops below a certain "turn-off" point, the switch contacts are opened and the compressor is switched off.
Thermostats of the type to which this invention relates typically employ a bellows communicating with a capillary tube in thermal contact with the location to be cooled. Expansion and contraction of a gas within the capillary tube and bellows causes corresponding expansion and contraction of the length of the bellows. The motion of the bellows is transmitted via an actuator to a switch element such as a bistable spring switch element which is capable of snapping between two stable positions, one of which closes a circuit and activates the compressor to cool the appliance and the other of which opens the circuit to deactivate the compressor. The spring switch element is fixed to one circuit element and extends outwardly toward another circuit element and carries a electrical contact on its free end. In the circuit open position of the spring switch element, the spring switch element is spaced away from the other circuit element. In the circuit closed position, the contact on the spring switch element engages a contact fixed to the other circuit element and the circuit is completed. Snapping of the spring switch element is controlled by the actuator in the thermostat which presses against the spring switch element with a force increasing with the increase in temperature above the set point detected within the appliance. Eventually, the force reaches a switch point at which the spring switch element snaps from one position to another to open or close the circuit.
Under certain circumstances, the temperature in an appliance compartment, for example, can continue to rise above the temperature set point even though the cold control has called for the compressor to cool the compartment. In these instances, an audio or visual indication of the excessive temperature condition is desired. Unfortunately, presently available alarm circuits require an increase in force to close the alarm circuit and cause additional electrical loading during closure of the circuit. This prevents the user from calibrating the alarm threshold temperature very closely to the thermostat's temperature set point for turning on the compressor.
Commonly assigned U.S. Pat. Nos. 3,065,320, 3,065,323, 3,648,214, 4,490,708, 5,142,261 and 5,585,774, the entire disclosures of which are incorporated herein by reference, are examples of thermostats for refrigeration appliances.